FRED ALERT! Freddy Garcia walks off the mound after he was hooked in the second inning of the Yankees’ 15-9 victory yesterday over the Red Sox. Garcia is in danger of being bumped from the rotation when Andy Pettitte returns. (NY Post: Charles Wenzelberg)

(NY Post: Charles Wenzelberg; Anthony J. Causi)

BOSTON — The 39-year-old guy is on a steady road to the Yankees’ rotation, the 23-year-old is further away.

It is not a wash.

Obviously the Yankees want Andy Pettitte back, love the idea of re-inserting his ability and temperament onto the roster. Especially because Pettitte has resembled the pitcher he was upon his 2010 exit, according to the Yankees’ reports of his minor league outings.

But Pettitte was a fringe benefit who fell into the Yankees’ lap with spring training nearly over. He was not in the plans.

Michael Pineda was — for today, and a long time to come. After Pineda’s acquisition, Brian Cashman had tried to lower the pressure around the young right-hander, insisting Pineda had much to learn and was not yet a top-of-the-rotation finished product.

But remember the Yankees general manager also likened Jesus Montero as a hitter to Miguel Cabrera and Hector Noesi to Pedro Astacio. And you do not trade the young, inexpensive versions of Cabrera and Astacio — as the Yankees did in obtaining Pineda from Seattle — unless you think you are getting a horse to ride for the next decade.

Now, who knows when (if?) Pineda even will pitch as a Yankee. Much less if he will be effective.

His Yankees career is on a scary Pavano-esque trajectory — unproductive and unhealthy. He showed up overweight to spring, didn’t pitch well, was shut down with a “mild” case of shoulder tendinitis and now — after throwing 15 pitches in extended spring yesterday — had to be shut down again due to more shoulder pain.

He will be in New York tomorrow for a dye-contrast MRI exam to see if the initial MRI missed something because, as Cashman said, “there is no sugarcoating this.”

“This is an unknown,” he said. “You treat the patient, not the MRI. Because the MRI was clean. So now we will dig down deeper with a more invasive test because the patient continues to hit a wall for whatever reason. … The bottom line is we are concerned because we don’t know what this is.”

And what the Yankees don’t know is killing them. Because Montero was a bullet they could fire just once. They needed to maximize him. This can’t be Jay Buhner to Seattle for Ken Phelps.

But when I asked Cashman if he regretted making the January deal, he said, “I would never say that. I made the trade, which means we were comfortable making the trade. He is ours now, and we have to do what we can to get him healthy. I am not going to look back at the decisions we made. We did a full physical [as part of the trade]. Right now, he has a shoulder problem and we have to figure out why.”

What the Yankees know for sure now is Pineda is not close to unseating anyone from what has — save Ivan Nova — been a shaky rotation. Freddy Garcia’s third terrible effort yesterday (five runs in 1 1/3 innings) completed three full turns of a rotation that now has a 5.84 ERA and a major league-worst .923 OPS against.

That the Yankees are not being undermined by their rotation, like the Red Sox have been, owes much to brilliant work from the bullpen and a power-packed lineup that made up a nine-run deficit with 15 unanswered runs in a 15-9 victory that made life even more uneasy for the 4-10 Red Sox and their manager Bobby Valentine.

Nevertheless, the Yankees cannot endure this rotation production for 162 games. Pettitte and Pineda loomed as potential upgrades, particularly if Garcia and Phil Hughes continued to pitch so poorly. Now it is just Pettitte, who is scheduled to pitch at Double-A on Wednesday. The Yankees hope he will follow with two starts after that of 100 pitches and then be ready for The Show on roughly May 10.

If he is close to vintage Pettitte — a full array of pitches and the fortitude to execute them under duress — he will be a blessing to a team with an annual mandate to win, just like he always was. But the Yankees also have been thinking long term more, especially with plans to drop under the $189 million luxury tax threshold for 2014. Pineda was central to those efforts. And, regardless of the post-trade spin, Pineda also was viewed as a major component for the 2012 team.

Now he is a guy with continuing shoulder pain, more tests on the docket and zero starts as a Yankee. Indeed, there is no sugarcoating that.